There are three main global temperature histories: the combined CRU-Hadley record (HADCRU), the NASA-GISS (GISTEMP) record, and the NOAA record. All three global averages depend on the same underlying land data archive, the Global Historical Climatology Network (GHCN). CRU and GISS supplement it with a small amount of additional data. Because of this reliance on GHCN, its quality deficiencies will constrain the quality of all derived products.

Figure 1-10: Changes (“delta”) in the global average temperature resulting from GHCN adjustments. Figure based on comparison of gridcells where both raw and adjusted data were present. data source: GHCN. See Appendix for calculation details.